Researchers and program planners have begun to recognize the influence of gender inequities on women's reproductive health, including women's susceptibility to HIV and other sexually transmitted infections (STIs). Gender-based power is likely to influence women's susceptibility to STIs by limiting their decision-making power within relationships, including decision-making regarding use of barrier methods, by constraining their access to information and health services, and in numerous other ways. Thus, in order to be effective, STI prevention efforts must address gender-based power. However, despite a growing body of research on the effect of gender-based power on women's reproductive health, critical gaps remain, including the need to examine gender-based power at the level of the individual, couple, community and society and the need for empirical data linking modifiable aspects of gender-based power to susceptibility to HIV and STIs. Our project, "Gender, power, and susceptibility to HIV/STIs in India," will address these and other gaps. Building on formative qualitative research, we will recruit a cohort of 670 married women and their husbands in Bangalore, India, and follow them for one year to identify modifiable aspects of gender-based power associated with a range of HIV/STI susceptibility outcomes. After this quantitative component, we will conduct post- study qualitative research (focus groups and in-depth interviews) to illuminate the results of the quantitative analyses. Our goals are to characterize women's power and identify aspects of gender-based power (including men's perspectives and practices) that are associated with: susceptibility to HIV and STIs; choice, use, and continued use, after counseling, of male and female condoms; and infection with STIs and HIV (among those willing to test for these outcomes). Based on our results, we will also identify the characteristics of context-appropriate interventions aimed at enhancing women's power (e.g., enhancing women's economic power or preventing gender-based violence) and those that promote physical or chemical barrier methods (including the design of education/counseling components and recruitment strategies). As part of this latter aim, we will determine the proportion of individuals who are willing to undergo HIV and STI testing and will identify characteristics, including those related to gender-based power, of those who decline to undergo such testing.